[lammps-users] help:Difference between s and p boundary.

Dear Lammps Users:
I’m currently simulating a system containing 2468 Ag particles, The Boundary has all been set to s in three dimensions.NVT integrator has been applied during the run,After heating it up to about 1400K. the Ag begin to melt and finally shaped a “droplet”,but I find a abnormal phenomenon,that is durint the simulation,the pressure usually statistically is a constant,about 0 bar,however ,the volume seems to change during the run,which is queer in contract to that in the periodical conditions . Is there something wrong ?

ChenJi

Material Science And Engineering Department
Xi’An Technological University
Xi’An,ShanXi Province,710032
P.R.C.

This is what I think might be happening. Steve please correct me if I am wrong.

Since you are using s bomdary conditions, the volume will change to emcompass all the atoms. If one of the atoms move out of the droplet and wants to wander around isolated, the volume would need to change accordingly. The pressure is essentially calculated due to inter-atomic interactions and forces. Once the droplet is formed, it is quite stable. The atoms (almost all of them) dont want to leave the droplet and remain in the vicinity of the equilibrium distances resulting in the static value of the pressure.

Vikas

2009/9/29 limitworld <[email protected]…127…>

Since you have all free surfaces, there is no imposed
pressure, so the atoms (lattice) will expand
however it likes - the pressure could well go to 0.

Be sure to visualize your system to insure your
box does not become huge if atoms evaporate
and drift away.

Steve

2009/9/29 limitworld <[email protected]>: